Air defrost air curtain display case

ABSTRACT

A multiple recirculating curtain refrigerated display case specially constructed to achieve low power air defrost. The defrosting function occurs by ambient air being drawn into the innermost passage through both ends, i.e., the air curtain outlet nozzle and the air curtain inlet, then across the refrigeration evaporator unit from both ends, to exhaust conduits near the coil midpoint and blowers forcing the air out through controlled trap doors to the ambient atmosphere.

United States aten r191 Beckwitli et al.

[451 Nov. 26, 1974 AIR DEFROST AIR CURTAIN DISPLAY CASE [75] Inventors: Sterling Beckwith, Menlo Park,

Calif.; William C. Johnston, Atlanta, Ga.

[73] Assignee: Kysor Industrial Corporation,

Cadillac, Mich.

[22] Filed: Apr. 5, 1974 [21] Appl. No.: 458,104

[52] US. Cl 62/82, 62/89, 62/256,

62/282, 62/458 [51] Int. Cl. F25d 21/12 [58] Field of Search 62/82, 89, 256, 282, 458

[56] References Cited UNITED STATES PATENTS 3,082,612 3/1963 Beckwith 62/282 3,403,525 10/1968 Beckwith ..62/256 Primary Examiner-William J. Wye Attorney, Agent, or Firm-Price, Heneveld, Huizenga & Cooper [5 7] ABSTRACT A multiple recirculating curtain refrigerated display case specially constructed to achieve low power air defrost. The defrosting function occurs by ambient air being drawn into the innermost passage through both ends, i.e., the air curtain outlet nozzle and the air curtain inlet, then across the refrigeration evaporator unit from both ends, to exhaust conduits near the coil midpoint and blowers forcing the air out through controlled trap doors to the ambient atmosphere.

13 Claims, 6 Drawing Figures PATENTL 13: 2 61974 SHEEV 1%? Q WW o AIIII.

A m & IWV

AIR DEI ROST AIR CURTAIN DISPLAY CASE BACKGROUND OF THE INVENTION This invention relates to air curtain type refrigerated display cabinets, and more particularly to a novel air defrost refrigerated display cabinet.

Multiple air curtain refrigerated display cases or cabinets have, since the pioneering development of such in the late 1950s and early 1960s by E. W. Simons, S. Beckwith, W. Hagen, R. Vogel, and others, gained wide acceptance in the food market industry. Such cabinets provide tremendous advantages in the storage and display of frozen foods and the like. The cabinets generally employ two or three air curtains, with the innermost one and the adjacent one normally being recirculated around the cabinet through passages. The innermost-curtain is normally the coldest, ,the second one being somewhat warmer, and the third outer one being basically an ambient temperature curtain to reinforce the jet inertia and warm the aisle. Refrigeration means, normally in the form of one or more evaporator coil units, is located in the innermost passage for cooling the air flowing past. Periodically during operation, this innermost passage and its refrigeration means must be defrosted to remove accumulated ice, frost, and condensation collected from the cooled air and tending to 'impede the operation of the equipment. Such defrosting is usually achieved with electrical heaters adjacent the coils of the refrigeration means, or in some instances, by passing hot gas through the coils of the refrigeration means. Hot gas defrost is complex, and is practical in only a small percentage of the installations, however. With electrical defrost, the refrigeration operation is temporarily halted, allowing the recirculating air curtain to be warmed by the high voltage electrical heaters. This normally requires special wiring from the compressor room and, because of the high wattage, is normally operated at higher voltage than the rest of the electrical components of the case. The warm air can then melt the frost, snow and/or ice built up in the air curtain inlet, on the evaporator coils and fins, in the passage, and on the outlet nozzle. It is important to melt this frost, etc. as rapidly as possible in order to minimize thawing of the frozen food products, and to minimize collection of frost on the frozen food products from the higher humidity in the recirculated warm air. To achieve this rapid defrosting necessitates the use of considerable electrical power, as is understandable, but has been necessary to this time.

Several years ago, some attempts were made to defrost the display cabinet by circulating ambient air through the inlet and coil zones of the inner passage (US. Pat. No. 3,082,612), or the inlet, coil, and back zones of the inner passage (US. Pat. No. 3,403,525), using internal baffles to block off the discharge end of the passage. Unfortunately, neither of these concepts proved practical and, as a consequence, all of the thousands of multiple curtain display cabinets manufactured use either the electrical defrost or, in a small percentage of cases, the hot gas defrost technique.

SUMMARY OF THE INVENTION An important object of this invention is to provide a multiple curtain, open front refrigerated display case or cabinet capable of rapid defrosting of the refrigeration means, the inner passage, and the air curtain inlet and outlet nozzles, using ambient air, without the complexities of the hot gas system, and without periodically demanding large amounts of electrical power as at present. The novel combination case is specially constructed to draw ambient air through it in a unique fashion from opposite ends for defrosting, and of achieving defrost in a time period as short as or shorter than that required for high energy electrical defrost. This rapid defrost is achieved by a special arrangement of components relative to the evaporator coils and air flow passages. Power consumption required for defrost has been proven to be only a fraction of that previously required, such that total power consumption of the display is lowered considerably.

The novel display cabinet, during defrost, has warm ambient air drawn into both the inlet and the outlet nozzle of the innermost air curtain, the air being passed through the refrigeration evaporator unit from opposite directions, and out special exhaust conduits intermediate the ends of the refrigeration unit, drawn by blowers that force the defrosting air out controlled trap doors to the ambient atmosphere. Defrosting by pulling warm air into the outlet face of the evaporator coil as well as into the inlet face reduces the length of the warm air path and thus speeds defrost.

Additional objects, advantages and features of the invention will become apparent from the following de tailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational, sectional view of the novel display cabinet;

FIG. 2 is a fragmentary perspective view of the top of the cabinet in FIG. 1;

FIG. 3 is a perspective view of the rear of the novel cabinet, with certain housing components removed;

FIG. 4 is an enlarged, fragmentary, perspective view of the inside of the cabinet with certain panels removed;

FIG. 5 is a perspective view of the evaporator coil unit, showing the position of defrost air outlets therefrom; and

FIG. 6 is a fragmentary enlarged sectional view of the upper right portion of the cabinet in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now specifically to the drawings, the novel refrigerated display cabinet assembly 10 includes a food storage and display space 12 defined by an upper panel or ceiling 14, a rear wall 16, and a bottom 18, the front having an enlarged access opening 20 communicating between storage space 12 and the ambient atmosphere 22 normally in a grocery store or supermarket. End panels 24 (FIG. 3) enclose the opposite ends of the storage area. Rear wall 16 preferably is slightly downwardly forwardly sloping, having a plurality of shelves 26 mounted generally normal thereto, i.e., having a slightly forwardly upward slope for optimum display of products. Extending around and adjacent the bottom, back, and top of the display area is an inner refrigerated air flow passage 28. It has an elongated air flow inlet 30 extending along the lower edge of access opening 20, covered by a perforate grid 32. It also has an elongated air flow outlet nozzle 34 extending along the upper edge of the access opening, opposite inlet 30. Outlet nozzle 34 contains air directing means such as honeycomb. Within passage 28, preferably along the lower side thereof, is a series of motor operated fans 36 acting as air propulsion means to constantly circulate the air through the passage 28, (in counterclockwise fashion as depicted in FIG. 1,) out nozzle 34, across the open front of storage area 12, and back into inlet member 30. In the lower rear portion of passage 28 is elongated evaporator type refrigeration coil unit 40 containing the usual sets of coils 42 and fins 44 as depicted in FIG. 5. These extend along the length of the back, and are arranged vertically in a plurality of banks, here three, one above the other. This evaporator refrigeration unit is operably connected with conventional compressor equipment (not shown) externally of the display case in usual fashion. Passage 28 is basically defined between the noted panels 14, 16 and 18 and a spaced partition 50 extending around the bottom, back, and top of the case. Panel 50 not only forms outer wall of inner passage 28, but also forms inner wall of a second adjacent passage 52 which likewise extends around the bottom, back and top of the case adjacent passage 28. Passage 52 has an elongated outlet nozzle 54 along the upper edge of the access opening, outwardly of inner nozzle 34. It includes air directing means such as honeycomb. This outlet nozzle 54 is at a small acute angle to nozzle 34 and cooperates with an elongated inlet 56 on the lower edge of the opening. Inlet member 56 is generally adjacent inlet 30, outwardly of the storage area, and has a perforate protective grid 58 thereover. Passage 52 includes a series of motor operated fans 60 for propelling the air through the passage, out outlet 54, across the face of the storage space adjacent the inner refrigerated air curtain, and through inlet 56 for recirculation. The guard curtain of air recirculated in this fashion is at a temperature higher than the temperature of the inner refrigerated air curtain but, normally below ambient temperature. A third curtain of air at ambient temperature is preferably also employed. This third curtain does not recirculate around the case as the first and second curtains do. It includes a series of inlets 64 at the top of the case, in which are mountedmotor operated fans 66 communicating with a passage 68 and an elongated outlet nozzle 70 outwardly of and adjacent nozzle 54 and preferably at a small acute angle thereto. This ambient air curtain is passed over opening outwardly of the two air curtains from outlet nozzles 34 and 54 and flows into aisle area 72 in front of the lower front wall 74 of the case, to cause an aisle warming effect as well as participating in this multiple air curtain action.

Basically, the construction described above is the normal construction shown in prior patents, and to which the following components are added to effect a new combination.

Specifically, protruding through panel 50 and the outer panel 80 is a series of spaced defrost air exhaust conduits 82 that communicate between passage 28 adjacent refrigeration evaporative coils 40 and a plenum chamber 86 at the rear of the case. Plenum 86 is defined between outer wall 80 and an L-shaped housing 90 extending upwardly at the back of the structure and over a portion of the top of the cabinet. Conduits 82 are arranged in a series along the back of the case or cabinet, each being small enough to allow proper air flow therearound of the curtain flowing through passage 52 therearound. The inner open ends of these conduits 82 are intermediate the upper and lower ends 40 and 40" respectively of the evaporator coils. Upper end 40' of the evaporative unit is basically oriented towards nozzle outlet 34, while lower end 40" is basically oriented towards inlet 30, i.e., oriented towards the air flow relative to the nozzle and inlet. Conduits 82 are preferably located closer to the upper end 40' of the coils than the lower end 40", with the optimum position having been found by experimentation to be about two thirds towards the upper end.

At the top of housing 90, along the length of the cabinet, is a series of air propelling and suction blowers 94 of conventional squirrel cage type, each having an axial inlet 94a and a tangential outlet 94b. Mounted on top of the housing is a series of trap doors 96, the forward edge of which is pivotally mounted at 98. Each trap door is located above one of the blowers. These trap doors are biased shut under normal conditions by their own weight, i.e., gravity, and are opened by air pressure from blowers 94 when operated. The trap doors are mounted to have the exhaust therefrom ejected upwardly and rearwardly, i.e., away from the ambient air inlet 64.

During the normal refrigeration operation of the display cabinet, the two recirculatory curtains of air are continuously propelled, the inner one by fans 36 through the evaporative cooling unit 40, out nozzle 34, across the front of the display area, and back into inlet 30, and the adjacent recirculatory guard curtain by fans 60, through the passage 52, out nozzle 54, across the open front, and into inlet 56. The ambient air curtain is drawn by blowers 66 through inlets 64, through passage 68 and out nozzle 70 across the front of the display area. (See solid arrows) During this operation, no flow occurs through conduits 82 and plenum 86, the trap doors 96 being closed and the blowers 94 being inactive.

Periodically, the frost build-up on the evaporator coil portions, and in passageway 28 as well as the outlet nozzle 34 and the inlet 30 requires momentary defrosting to enable the unit to operate at reasonable efficiency. The defrosting operation may be manually activated, or more commonly, will be activated on a time or temperature controlled basis. This defrosting must be done rapidly, without thawing the frozen food products or the like in the display area, or creating a heavy frost layer on the food products. With the novel assembly, during defrost, fans 36, and 66 continue to operate, while blowers 94 are activated. The positive pressure of blowers 94 forces trap doors 96 open for discharge of defrosting air. This air is drawn by these blowers into passage 28 from opposite directions simultaneously, i.e., into outlet nozzle 34 at the top front of the case and simultaneously into inlet 30 at the bottom front of the case, causing the air to flow in both directions through the inner passage 28 toward the evaporator coil unit. (See broken arrows) This is warm ambient air out of the room which quickly thaws the frost out of both the outlet nozzle and the inlet and out of both ends of the passage. This ambient air then enters both ends of the evaporator coil unit, i.e., upper end 40 and lower end 40" towards the central portions thereof, where it flows to and through outlet conduits 82. This air from both ends causes the evaporator coil, where most of the frost is concentrated, to defrost rapidly. The defrost air flows into plenum 86 and to blowers 94 which ejects them from the display case upwardly and rearwardly so as not to disturb customers in the store or the food products in the display area.

Extensive experimentation has shown that the conduits 82 operate most efficiently when positioned closer to the upper end 40 than the lower end 40" in the particular display case depicted. In fact, a position about two thirds of the way toward the upper end is optimum.

Experiemntation has shown that substantial savings can be achieved over present defrost mechanisms. Firstly, the defrost time can be lowered significantly, e.g., from approximately 1.5 hours per day to 0.8 hours per day when the case is converted from the conventional electric defrost to this novel air defrost system. The warm air does not need to slowly defrost its way from one end of the passage to the other and from one end of the evaporator coil to the other. As close as can be determined, approximately 0.73 kilowatt hours per day per foot of display case are saved using this system. l.e., approximately 266.5 kilowatt hours per year per foot of display case. When it is considered that there are literally hundreds of thousands of feet of display case of this type being used, and that every major manufacturer now makes .and markets this basic type of multiple curtain display case, the potential savings in energy for the country are significant. Moreover, the food products are kept in optimum condition during the defrosting operation, to the benefit of the customer. And, the initial cost of the unit is not significantly different from the initial cost of the electrical defrost unit.

Experimental operation has also shown that, by stopping blowers or fans 60 with starting of blowers 94, de frosting time is shortened even further, for a further reduction of about l8-20 percent. This can be accomplished by a correctional double electrical switch, e.g., a double throw relay.

Additional objects and advantages as well as minor variations in the construction depicted may well occur to those skilled in this art upon studying this disclosure. This invention is not intended to be limited strictly to the preferred form depicted and described as illustrative thereof, but only by the scope of the appended claims and the reasonable equivalents thereto.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. in an air curtain refrigerated display cabinet, said cabinet having an access opening in one side communicating a storage and display space within the cabinet with the ambient atmosphere, at least two outlet nozzles, an inner one and an adjacent one, extending across the upper edge of the access opening, and corresponding inner and adjacent inlet members extending across the lower edge of said opening; an inner passage and an adjacent passage connecting said inlet members with respective ones of said outlet nozzles; circulating means in each of said passages for circulating panels of air through said passages and across the access opening from said outlet nozzles to said inlet members; refrigeration evaporator coil means in said inner passage for cooling circulated air flowing therepast; the improvement comprising: air defrost means comprising a housing forming at least one plenum chamber; defrost air conduit means from said inner passage, adjacent said evaporator coil means, to said plenum chamber; air discharge outlet means from said plenum chamber to the ambient atmosphere; and air propulsion means operably associated with said plenum chamber, said conduit means, and said discharge outlet means arranged to simultaneously draw ambient defrost air into said inner outlet nozzle and into said inner inlet member, through said inner passage to said evaporator coil means, across said coil means from both directions, through said conduit means to said plenum chamber, and out said discharge outlet means to the ambient atmosphere.

2. The refrigerated display cabinet in claim 1 including trap doors over said air discharge outlet means, said trap doors being normally closed, and shiftable to open condition by air pressure from said propulsion means.

3. The refrigerated display cabinet in claim ll wherein said propulsion means comprise a plurality of blowers in said housing.

4. The refrigerated display cabinet in claim 1 wherein said evaporator coil means has a first end generally oriented toward said inner outlet nozzle and a second end generally oriented toward said inner inlet member; and said defrost air conduits are located intermediate said first and second ends.

5. The refrigerated display cabinet in claim a wherein said defrost air conduits are located closer said first end than said second end of said evaporator unit.

6. The refrigerated display cabinet in claim 1 wherein said evaporator coil means is located in the rear portion of said cabinet, said housing extends up the rear of said housing to the top, said air discharge outlet means are adjacent the top of said housing, and include air pressure responsive trap doors thereover.

7. The refrigerated display cabinet in claim 6 includ ing a third outlet nozzle extending across said access opening adjacent to and outwardly of said two outlet nozzles, ambient air inlets at the top of said cabinet, and passage means with air movement means therein, between said ambient air inlets and said third outlet nozzle: and said trap doors being arranged to open in a direction causing discharge of defrost air away from said ambient air inlets.

8. In a refrigerated display cabinet having an access opening in one side communicating a storage and display space within the cabinet with the ambient atmosphere, at least two outlet nozzles, an inner one and an adjacent one, extending across one edge of the access opening, and corresponding inner and adjacent inlet members extending across the opposite edge of the opening; an inner passage and an adjacent passage connecting said inlet members with respective ones of said outlet nozzles; circulating means for circulating panels of air through said passages and across the access opening from the outlet nozzles to the inlet members; refrigeration means in the innermost one of said passage means, having one end oriented generally toward said inner inlet member and a second end oriented generally toward said inner outlet nozzle; the improvement comprising: air defrost means for said refrigeration means and said inner passage means, nozzle, and inlet member, comprising exhaust conduit means communieating with said innermost passage means between the ends of said refrigeration means, and suction means communicating with said exhaust conduit means and exhausted to the ambient atmosphere, whereby, with actuation of said suction means, ambient air flows into the innermost outlet nozzle and into the innermost inlet member, through said refrigeration means from opposite directions, through said exhaust conduit means to the ambient atmosphere.

9. The refrigerated display cabinet in claim 8 wherein said exhaust conduit means includes portions extending from said innermost passage means through adjacent passage means.

10. The refrigerated display cabinet in claim 8 including a plenum chamber communicating with said exhaust conduit means and suction means, and trap door means from said plenum chamber, operably associated with said suction means to open only during actuation of said suction means.

11. The refrigerated display cabinet in claim 8 wherein said suction means constitues blowers in communication with said exhaust conduit means, and to the ambient atmosphere through trap door means; said trap door means being openable during operation of said blowers.

12. The refrigerated display cabinet in claim 11 wherein said trap door means are opened by air pressure generated by said blowers.

13. A method of air defrosting the passage and refrigeration means of an air curtain refrigerated display case having an open front with an outlet nozzle from the passage on one edge of the open front and an inlet member to the passage on the opposite edge, comprising the steps of:

drawing ambient defrosting air into the passage from opposite directions through the outlet nozzle and through the inlet member, drawing such air across the refrigeration means from opposite ends thereof, and discharging such air intermediate the ends of the refrigeration means and out of the display case. 

1. In an air curtain refrigerated display cabinet, said cabinet having an access opening in one side communicating a storage and display space within the cabinet with the ambient atmosphere, at least two outlet nozzles, an inner one and an adjacent one, extending across the upper edge of the access opening, and corresponding inner and adjacent inlet members extending across the lower edge of said opening; an inner passage and an adjacent passage connecting said inlet members with respective ones of said outlet nozzles; circulating means in each of said passages for circulating panels of air through said passages and across the access opening from said outlet nozzles to said inlet members; refrigeration evaporator coil means in said inner passage for cooling circulated air flowing therepast; the improvement comprising: air defrost means comprising a housing forming at least one plenum chamber; defrost air conduit means from said inner passage, adjacent said evaporator coil means, to said plenum chamber; air discharge outlet means from said plenum chamber to the ambient atmosphere; and air propulsion means operably associated with said plenum chamber, said conduit means, and said discharge outlet means arranged to simultaneously draw ambient defrost air into said inner outlet nozzle and into said inner inlet member, through said inner passage to said evaporator coil means, across said coil means from both directions, through said conduit means to said plenum chamber, and out said discharge outlet means to the ambient atmosphere.
 2. The refrigerated display cabinet in claim 1 including trap doors over said air discharge outlet means, said trap doors being normally closed, and shiftable to open condition by air pressure from said propulsion means.
 3. The refrigerated display cabinet in claim 1 wherein said propulsion means comprise a plurality of blowers in said housing.
 4. The refrigerated display cabinet in claim 1 wherein said evaporator coil means has a first end generally oriented toward said inner outlet nozzle and a second end generally oriented toward said inner inlet member; and said defrost air conduits are located intermediate said first and second ends.
 5. The refrigerated display cabinet in claim 4 wherein said defrost air conduits are located closer said first end than said second end of said evaporator unit.
 6. The refrigerated display cabinet in claim 1 wherein said evaporator coil means is located in the rear portion of said cabinet, said housing extends up the rear of said housing to the top, said air discharge outlet means are adjacent the top of said housing, and include air pressure responsive trap doors thereover.
 7. The refrigerated display cabinet in claim 6 including a third outlet nozzle extending across said access opening adjacent to and outwardly of said two outlet nozzles, ambIent air inlets at the top of said cabinet, and passage means with air movement means therein, between said ambient air inlets and said third outlet nozzle: and said trap doors being arranged to open in a direction causing discharge of defrost air away from said ambient air inlets.
 8. In a refrigerated display cabinet having an access opening in one side communicating a storage and display space within the cabinet with the ambient atmosphere, at least two outlet nozzles, an inner one and an adjacent one, extending across one edge of the access opening, and corresponding inner and adjacent inlet members extending across the opposite edge of the opening; an inner passage and an adjacent passage connecting said inlet members with respective ones of said outlet nozzles; circulating means for circulating panels of air through said passages and across the access opening from the outlet nozzles to the inlet members; refrigeration means in the innermost one of said passage means, having one end oriented generally toward said inner inlet member and a second end oriented generally toward said inner outlet nozzle; the improvement comprising: air defrost means for said refrigeration means and said inner passage means, nozzle, and inlet member, comprising exhaust conduit means communicating with said innermost passage means between the ends of said refrigeration means, and suction means communicating with said exhaust conduit means and exhausted to the ambient atmosphere, whereby, with actuation of said suction means, ambient air flows into the innermost outlet nozzle and into the innermost inlet member, through said refrigeration means from opposite directions, through said exhaust conduit means to the ambient atmosphere.
 9. The refrigerated display cabinet in claim 8 wherein said exhaust conduit means includes portions extending from said innermost passage means through adjacent passage means.
 10. The refrigerated display cabinet in claim 8 including a plenum chamber communicating with said exhaust conduit means and suction means, and trap door means from said plenum chamber, operably associated with said suction means to open only during actuation of said suction means.
 11. The refrigerated display cabinet in claim 8 wherein said suction means constitutes blowers in communication with said exhaust conduit means, and to the ambient atmosphere through trap door means; said trap door means being openable during operation of said blowers.
 12. The refrigerated display cabinet in claim 11 wherein said trap door means are opened by air pressure generated by said blowers.
 13. A method of air defrosting the passage and refrigeration means of an air curtain refrigerated display case having an open front with an outlet nozzle from the passage on one edge of the open front and an inlet member to the passage on the opposite edge, comprising the steps of: drawing ambient defrosting air into the passage from opposite directions through the outlet nozzle and through the inlet member, drawing such air across the refrigeration means from opposite ends thereof, and discharging such air intermediate the ends of the refrigeration means and out of the display case. 